1. Field of the Invention
The present invention relates to a modular switching network for time-division telephone exchanges using the pulse code modulation technique. The present invention relates more particularly to small-capacity exchanges or switches, making use of concentrator-deconcentrator devices.
2. Description of the Prior Art
Conventional switching networks consist of complex assemblies of circuits known as time-division switches and space-division switches occupying much of the volume of exchanges including them. In addition, these complex assemblies are ill-adapted to the production of easily extensible small-capacity exchanges.
The size of switching networks may be reduced by the use of concentration techniques based on the fact that not all subscribers use their lines at the same time, making it possible to connect to an exchange a number of subscribers greater than the total number of inputs to the switching network of this exchange.
Concentration techniques are implemented by means of concentrator-deconcentrator devices, one of these devices embodying time-division switching arrays known as symmetrical time-division arrays. This concentrator-deconcentrator device includes a centralized part comprising a central module consisting of symmetrical time-division arrays and which connect subscribers to a switch in order to ensure communication with subscribers who are not dependent on the concentrator-deconcentrator device.
This concentrator-deconcentrator device comprises at the same time a centralized concentrator part and a decentralized concentrator part for ensuring communications in both directions, these parts being located in the terminal modules which comprise the subscriber and auxiliary line connecting units and which constitute what is conventionally known as a subscriber and trunk line connecting unit.